Ferroelectric thin films based on domain switching have been demonstrated to be a promising media for Probe-Based Data Storage (PDS) based data storage devices. Both single and polycrystalline ferroelectric thin films have been investigated. In some cases, the smallest bit size (or data density) may be limited by the domain size for single crystal films, and by the grain size for poly-crystalline films. For ferroelectric thin films, scaling of switchable domain size (or bit size) below about 25 nm becomes very difficult due to defects in the grown thin films.